This invention relates to a power transmission device for transmitting the turning torque of an engine to vehicle wheels through a transmission.
In a power transmission device for transmitting the turning force of an engine to a transmission through a torque converter, since the torque converter has a creeping function, smooth start is possible. Also, start on an upward slope is easy. But there is a problem that since slip is produced between the input and the output, transmission efficiency and thus fuel economy are bad.
In order to solve this problem, JP patent publication 2000-310260 proposes a power transmission device in which a slip control type clutch comprising a wet type multiple disc clutch and a wedge force control type clutch comprising a roller clutch are provided between an input shaft, to which the turning torque of the engine is transmitted, and an output shaft. At the start, the wet type multiple disc clutch is engaged to transmit the rotation of the input shaft to the output shaft while producing slip. When the turning torque of the output shaft reaches a preset value or the difference in the number of revolutions between the input shaft and the output shaft drops below a predetermined value, the wedge force control type clutch is engaged, and thereafter the slip control type clutch is disengaged.
In the prior art power transmission device, since at the start, the slip control type clutch is engaged to transmit the turning torque between the input shaft and the output shaft while producing slip, smooth start is possible. Also, since the wedge force control type clutch is engaged after the slip control type clutch is engaged, the engaging time of the slip control type clutch may be short. Thus it is possible to reduce energy loss and improve fuel economy.
In the prior art power transmission device, when the brake pedal is released for restart in a stopped state on an upward slope, a turning torque in an opposite direction to the revolving direction of the engine is transmitted from the wheel side to the output shaft, so that the vehicle body moves in a direction opposite to the advancing direction. This makes it difficult to start on a slope.
Also, when the wedge force type clutch is engaged, rollers mounted in wedge-shaped spaces impulsively bite into narrow portions of the wedge-shaped spaces, so that engaging shock is produced.
An object of this invention is to provide a power transmission device in which a control type slip clutch and a mechanical type control type two-way clutch using engaging elements such as rollers are mounted between an input shaft and an output shaft and which makes easy start on a slope and absorbs engagement shock of the control type two-way clutch.
According to this invention, there is provided a power transmission device comprising an input shaft to which the turning torque of an engine is transmitted, an annular output shaft mounted coaxially with the input shaft for transmitting the turning torque transmitted from the input shaft to vehicle wheel side, a control type slip clutch mounted between the input shaft and the output shaft for engaging the input shaft and the output shaft together while producing slip, a mechanical type control type two-way clutch using engaging elements for engaging the input shaft and the output shaft together after the control type slip clutch has been engaged, and a one-way clutch provided between the output shaft and a stationary member provided radially outside of the output shaft for engaging the output shaft with the stationary member to lock the output shaft when a turning torque in an opposite direction to the rotating direction of the engine is transmitted to the output shaft from the vehicle wheel side.
By providing a one-way clutch between the output shaft and the stationary member provided outside thereof, when depressing of the brake pedal is released in a stopped state on an upward slope, rotation in the opposite direction to the revolving direction of the engine is transmitted to the output shaft from the vehicle wheel side, so that the one-way clutch is engaged, thereby locking the output shaft. Since the output shaft is locked, the vehicle body is prevented from moving in the reverse direction to the moving direction. This makes start on a slope easy.
As the one-way clutch, a one-way roller clutch may be used which locks the output shaft by engaging rollers into narrow portions of wedge-shaped spaces.
In the power transmission device according to said invention, by providing a rotation shock absorbing damper for damping shocks in a rotational direction in a power transmission line for transmitting turning torque from the engine to the input shaft, it is possible to absorb shocks when the rotation of the engine is transmitted to the input shaft. Thus, it is possible to smoothly transmit rotation of the engine to the input shaft.
As the control type slip switch, a wet type multiple disc clutch may be used. On the other hand, as the control type two-way clutch, a control type two-way roller clutch may be used which controls the rotation of a retainer mounted between the input shaft and the output shaft, thereby engaging rollers retained by the retainer into narrow portions of wedge-shaped spaces to transmit the rotation of the input shaft to the output shaft.
By providing the control type two-way clutch with a clutch outer ring and fitting the clutch outer ring on the inner periphery of the output shaft with a small clearance, the clutch outer ring is elastically deformed diametrically outwardly and pressed against the inner peripheral surface of the output shaft when engaging elements engage the outer periphery of the input shaft and the inner periphery of the clutch outer ring. Thus, it is possible to absorb shocks upon engagement by action of the elastic deformation of the clutch outer ring and the slip until the clutch outer ring and the output shaft engage together.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: